Refactor en passant logic and improve test clarity

Refactor board logic and improve tests

- Refactor import statements in pieces.go
- Add String method to Piece type for better representation
- Add isEnPassant field to Move struct
- Update move logic to mark en passant captures
- Adjust handling of pawn moves related to en passant
- Change MakeMove to not return a move
- Update applyEnPassant to accept pointer to Move
- Track en passant captures within Move struct
- Remove redundant condition check in UndoMove
- Enhance readability of variable assignments
- Comment out parallel test execution for debugging
- Modify error handling for accurate performance logging
- Correct expected board state after undo in en passant scenario
- Clarify comments in tests regarding en passant logic
- Improve clarity of error messages in test assertions

board/board.go

@@ -76,7 +76,7 @@ func (board Board) Move(from Coordinate, to Coordinate) {
 	board.Board[fromRow][fromCol] = 0
 }
 
-func (board *Board) MakeMove(move Move) Move {
+func (board *Board) MakeMove(move Move) {
 	board.WhiteCastleHistory = append(board.WhiteCastleHistory, board.WhiteCastling)
 	board.BlackCastleHistory = append(board.BlackCastleHistory, board.BlackCastling)
 	board.PreviousEnpassant = board.EnPassant
@@ -95,7 +95,7 @@ func (board *Board) MakeMove(move Move) Move {
 			board.Set(move.to, move.promotionTo|move.piece.GetColor())
 		}
 
-		board.applyEnPassant(move)
+		board.applyEnPassant(&move)
 	}
 
 	castlability := &board.WhiteCastling
@@ -122,7 +122,7 @@ func (board *Board) MakeMove(move Move) Move {
 
 	board.Active = (^board.Active).GetColor()
 	board.Moves = append(board.Moves, move)
-	return move
+	// return move
 }
 
 func (board *Board) UndoMove() {
@@ -135,8 +135,10 @@ func (board *Board) UndoMove() {
 		castling = &board.BlackCastling
 	}
 
+	toRow, toCol := move.to.GetCoords()
+	fromRow, _ := move.from.GetCoords()
+
 	if move.IsCastle() {
-		toRow, toCol := move.to.GetCoords()
 
 		if toCol == 0 {
 			castling.CanQueenSide = true
@@ -150,12 +152,15 @@ func (board *Board) UndoMove() {
 		}
 	}
 
+	if move.isEnPassant {
+		board.Set(move.to, 0)
+		captured := CreateCoordByte(fromRow, toCol)
+		board.Set(captured, move.capture)
+	}
+
 	board.Active = (^board.Active).GetColor()
 	board.EnPassant = board.PreviousEnpassant
 	board.Moves = board.Moves[0 : len(board.Moves)-1]
-	if len(board.Moves) > 0 {
-		board.applyEnPassant(board.Moves[len(board.Moves)-1])
-	}
 	board.WhiteCastling = board.WhiteCastleHistory[len(board.WhiteCastleHistory)-1]
 	board.BlackCastling = board.BlackCastleHistory[len(board.BlackCastleHistory)-1]
 
@@ -163,7 +168,7 @@ func (board *Board) UndoMove() {
 	board.BlackCastleHistory = board.BlackCastleHistory[0 : len(board.BlackCastleHistory)-1]
 }
 
-func (board *Board) applyEnPassant(move Move) {
+func (board *Board) applyEnPassant(move *Move) {
 	toRow, toCol := move.to.GetCoords()
 	fromRow, fromCol := move.from.GetCoords()
 	if move.piece.GetType() != Pawn {
@@ -171,15 +176,16 @@ func (board *Board) applyEnPassant(move Move) {
 		return
 	}
 
-	enemyPiece := Pawn | (^move.piece).GetColor()
+	enemyPiece := Pawn | ((^move.piece).GetColor())
 	if board.EnPassant != nil && move.to == *board.EnPassant {
 		// En passant!
 		captured := CreateCoordByte(fromRow, toCol)
 		if board.Get(captured) != enemyPiece {
-			panic(fmt.Sprintf("En Passanted non-enemy piece on %v, got %v, expcted %v", captured, board.Get(captured), enemyPiece))
+			panic(fmt.Sprintf("En Passanted non-enemy piece on %v, got %v, expected %v", captured, board.Get(captured), enemyPiece))
 		}
 		board.Set(captured, 0)
 		move.capture = enemyPiece
+		move.isEnPassant = true
 	}
 	board.EnPassant = nil
 

board/board_test.go

@@ -218,7 +218,7 @@ func TestUndoMove(t *testing.T) {
 			board.UndoMove()
 
 			if board.GetStr("d6") != 0 {
-				t.Errorf("board failed to delete passanting pawn upon undo, expected %v, got %v", nil, board.GetStr("d6"))
+				t.Errorf("board failed to delete passanting pawn upon undo, expected %v, got %v", 0, board.GetStr("d6"))
 			}
 
 			if board.GetStr("d5") != Black|Pawn {

board/move.go

@@ -10,6 +10,7 @@ type Move struct {
 	piece       Piece
 	capture     Piece
 	promotionTo Piece
+	isEnPassant bool
 }
 
 func (move Move) IsCastle() bool {
@@ -221,7 +222,9 @@ func (game Board) getPawnMoves(coord Coordinate) []Move {
 		if int(enRow) == int(row)+direction {
 			diff := int(enCol) - int(col)
 			if diff == -1 || diff == 1 {
-				moves = append(moves, game.CreateMove(coord, *game.EnPassant))
+				move := game.CreateMove(coord, *game.EnPassant)
+				move.isEnPassant = true
+				moves = append(moves, move)
 			}
 		}
 	}

board/move_test.go

@@ -87,7 +87,7 @@ func TestGetMoves(t *testing.T) {
 func TestPerfs(t *testing.T) {
 	for name, test := range getPerfData() {
 		t.Run(name, func(t *testing.T) {
-			t.Parallel()
+			// t.Parallel()
 			start, err := FromFEN(test.FEN)
 
 			if err != nil {

board/pieces.go

@@ -1,6 +1,8 @@
 package board
 
-import "fmt"
+import (
+	"fmt"
+)
 
 type Piece byte
 
@@ -16,6 +18,10 @@ const (
 	King
 )
 
+func (piece Piece) String() string {
+	return string(piece.GetRune())
+}
+
 func GetPiece(c rune) (Piece, error) {
 	white := true
 	if c > 'Z' {